This first CEX you mentioned is actually the owner of CMC, so it's not surprising if it's really at the top because they use that platform for their own promotion. Given that the same CEX operates mainly in the gray zone, I would not be surprised if some of their acquisitions remained secret and that they own much more than what they admit.
However, if you ask me why their names start with "B", it probably has something to do with the fact that it is the first letter in the word "Bitcoin" - and it is no secret that Bitcoin sells a lot of junk (altcoins) that are listed on these platforms.
I can proudly say that I have never made a deposit at any of the aforementioned CEX, and I only have an account open at one, although that is a completely different story.
You obviously sound as if you are not inclined to centralized exchanges but the obviously they still have relevance in this crypto space particularly for off-ramp services
I've observed a trend where exchanges starting with the letter 'B' are consistently improving in global rankings on CoinMarketCap (CMC) and CoinGecko (CG).
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Think about all the crypto exchanges you've heard of. How many of them start with the letter "A"? Or any other letter, for that matter.
The answer to your question is rather obvious, considering that most crypto exchanges, particularly the older ones, begin with the letter "B".
I think the oldest crypto exchange on the list should be Bitstamp and Bitfinex. The rest are relatively young particularly Bitget who is just 5 years old in the industry.